Physically based modeling of rainfall-triggered landslides: a case study in the Luquillo forest, Puerto Rico

This paper presents the development of a rainfall-triggered landslide module within an existing physically based spatially distributed ecohydrologic model. The model, tRIBS-VEGGIE (Triangulated Irregular Networks-based Real-time Integrated Basin Simulator and Vegetation Generator for Interactive Evolution), is capable of a sophisticated description of many hydrological processes; in particular, the soil moisture dynamics are resolved at a temporal and spatial resolution required to examine the triggering mechanisms of rainfall-induced landslides. The validity of the tRIBS-VEGGIE model to a tropical environment is shown with an evaluation of its performance against direct observations made within the study area of Luquillo Forest. The newly developed landslide module builds upon the previous version of the tRIBS landslide component. This new module utilizes a numerical solution to the Richards' equation (present in tRIBS-VEGGIE but not in tRIBS), which better represents the time evolution of soil moisture transport through the soil column. Moreover, the new landslide module utilizes an extended formulation of the factor of safety (FS) to correctly quantify the role of matric suction in slope stability and to account for unsaturated conditions in the evaluation of FS. The new modeling framework couples the capabilities of the detailed hydrologic model to describe soil moisture dynamics with the infinite slope model, creating a powerful tool for the assessment of rainfall-triggered landslide risk.United States. National Aeronautics and Space Administration (Project NNX07AD29G

The Impact of Subsea Gas Releases and Resulting Gas Plumes Using techniques in Computational Fluid Dynamics

Presentatio

Exploration of indian social influence on civic architecture in post-colonial Durban: towards the design of an exhibition centre in Phoenix.

Masters Degree. University of KwaZulu-Natal, Durban.This research process has explored the impact of colonialism and apartheid on Indian civic space from a global perspective and then from a local perspective within the City of Durban. The justification for exploring Indian social influence was that Durban contains the largest number of Indian people outside of India. This study has focussed on social influences of culture and identity and how it impacted civic spaces in the built form. The architectural theories of Phenomenology and Critical Regionalism has further helped the development of a brief for the design of an Exhibition Centre in Phoenix. This typology has sought to restore a sense of belonging, pride, recognition and celebration of the Indian people by creating meaningful architecture in the civic realm. Colonialism has impacted India and South Africa, resulting in the loss of culture and identity of Indian communities. Therefore, by analysing India and South Africa's historical context, it was possible to compare their social and physical landscapes. Traditional Indian cities were very organic and sporadic; however colonial British influences had a Eurocentric grid iron structure; therefore, a fusion of these developments has guided the proposed civic development. The proposed Exhibition Centre incorporates aspects of Indian culture and identity as well as modern-day contemporary design concepts. The outlined precedent and case studies has helped to demonstrate the relationship between culture, identity and architecture, and has strengthened the overall design development process

The impact of the affirmative procurement policy on affirmable business enterprises in the South African construction industry.

Thesis (Ph.D.)-University of Natal, Durban, 2000.The construction industry in South Africa is envisaged to play a pivotal role in the reconstruction of the South African economy, via the delivery of economic and social infrastructure. The skewed ownership I patterns prevalent in the construction sector, resulted in the South African government utilising public sector procurement as a mechanism to address these imbalances, and to promote wider participation I in public sector construction opportunities. This dissertation analyses the role of the construction industry in South Africa, and explores the rationale behind utilising public sector procurement as a mechanism to promote wider participation in the construction industry in South Africa. The research then focuses on the application of the Affirmative Procurement Policy (APP) on construction projects procured by the National Department of Public Works, in order to evaluate the impact which this policy has had on the growth and development of Affirmable Business Enterprises (ABEs). The research evaluates the primary policy outcomes, via the development of appropriate indices and a diagnostic quadrant comparator, and concludes that the application of the APP has had a positive impact on ABE participation, with levels of participation varying across construction sub sectors and categories. It was also found that financial premiums, borne by the State in adopting this policy, were nominal when compared with the initial projected outcomes and the overall benefits. The overall performance of ABEs, measured against that of non-ABEs, was then tested to ascertain whether the adoption of the APP was a necessary and sufficient condition for ABE enablement and empowerment. The research concludes that there is a difference in overall performance between J ABEs and non-ABEs, and that supply side interventions and capacitation programmes are required to mitigate the increased risk exposure by the State, when engaging ABEs on construction projects. The : research also analyses the variation in the levels of participation of ABEs, in the different construction sub sectors and concludes that the manner in which ABEs are structured and their internal business processes tend to establish operational limitations, which influence their scope of activitiies to a larger extent than the existence of eternal sub sector thresholds. Similar characteristics were,observed in non-ABEs of a similar size, inferring that the problems encountered relate to business development and growth of small and medium enterprises, in general. The research also. analyses the impact that the APP has had on subcontracting relationships and the promotion of structured joint ventures. It concludes that whilst the requirements of the APP has seen the development of formalised subcontracting relationships, the form of subcontracts that are currently utilised do not comply with the requirements outlined in the APP, which are aimed at eradicating unfair subcontracting conditions. The adoption of the APP has seen an increase in structured joint ventures between ABEs and larger established contractors. The analysis of these joint ventures concludes that they provide an effective means of transferring expertise, provided that they are structured appropriately. The dissertation concludes with recommendations on APP policy refinements, mechanisms to enhance compliance and opportunities for international application. The recent enactment of the Preferential Procurement Policy Act (Act 5 of 20(0) in South Africa indicates that several elements of the APP are likely to be prescribed as mandatory requirements for public sector procurement by different government institutions and across the different industrial sectors. It is therefore important that the areas identified for further research be pursued, to ensure optimal policy outcomes across a range of industrial sectors

The role of rooting strategies on the eco-hydrology of semi-arid regions

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 193-205).Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. In particular, the rooting strategies employed by vegetation can be critical to their survival. However, land surface models currently prescribe rooting profiles as a function of only the plant functional type of interest with no consideration for the soil texture or rainfall regime of the region being modeled. Additionally, these models do not incorporate the ability of vegetation to dynamically alter their rooting strategies in response to transient changes in environmental forcings or competition from other plant species, and therefore tend to underestimate the resilience of these ecosystems. To address the simplicity of the current representation of roots in land surface models, a new dynamic rooting scheme was incorporated into the framework of the distributed ecohydrologic model tRIBS+VEGGIE. The new scheme optimizes the allocation of carbon to the root zone to reduce the perceived stress of the vegetation, so that root profiles evolve based upon local climate and soil conditions. The strength of this scheme lies in its ability to optimize the rooting profile in a computationally-efficient manner, without requiring additional parameterization by the model user. The ability of the new scheme to capture the complex dynamics of natural systems was evaluated by comparisons to hourly-timescale energy flux, soil moisture and vegetation growth observations from the Walnut Gulch Experimental Watershed, Arizona. Very good agreement was found between the model and observations, providing confidence that the improved model is able to capture the multidirectional interactions between climate, soil and vegetation at this site. The power of the new scheme was demonstrated through simulation of observed forms of within-hillslope vegetation patterning and the model's ability to represent competition-colonization dynamics between different plant functional types under non-equilibrium conditions.by Gajan Sivandran.Ph.D

The Impact of Subsea Gas Releases and Resulting Gas Plumes Using Computational Fluid Dynamics

PresentationA Computational Fluid Dynamics (CFD) model was developed to describe the behavior of a subsea gas release and the subsequent rising gas plume. Four numerical approaches were assessed for their suitability to capture the characteristic behaviors in a rising gas plume by comparing the CFD results with experimental data obtained from an underwater gas release experiment carried out in a 10 m depth towing tank basin. The k-ε turbulence model was found to be unsatisfactory in capturing random wandering behavior of the subsea gas plume due to the inherent Reynolds-Averaged Navier-Stokes (RANS) nature of the approach. The result is an over-prediction of the plume central line velocity and an under-prediction of the plume width as there was no mechanism to distribute and dissipate the high momentum gained during the initial gas release phase. The results obtained using the Large Eddy Simulation (LES) approach show the inherently random wandering behavior of the plume is successfully captured and both the centerline velocity and the velocity profile are in much better agreement with the experimental data

Interdependence of climate, soil, and vegetation as constrained by the Budyko curve

The Budyko curve is an empirical relation among evapotranspiration, potential evapotranspiration and precipitation observed across a variety of landscapes and biomes around the world. Using data from more than three hundred catchments and a simple water balance model, the Budyko curve is inverted to explore the ecohydrological controls of the soil water balance. Comparing the results across catchments reveals that aboveground transpiration efficiency and belowground rooting structure have adapted to the dryness index and the phase lag between peak seasonal radiation and precipitation. The vertical and/or lateral extent of the rooting zone exhibits a maximum in semi-arid catchments or when peak radiation and precipitation are out of phase. This demonstrates plant strategies in Mediterranean climates in order to cope with water stress: the deeper rooting structure buffers the phase difference between precipitation and radiation. Results from this study can be used to constrain land-surface parameterizations in ungauged basins or general circulation models

Influence of soil and climate on root zone storage capacity

Root zone storage capacity (Sr) is an important variable for hydrology and climate studies, as it strongly influences the hydrological functioning of a catchment and, via evaporation, the local climate. Despite its importance, it remains difficult to obtain a wellâ founded catchment representative estimate. This study tests the hypothesis that vegetation adapts its Sr to create a buffer large enough to sustain the plant during drought conditions of a certain critical strength (with a certain probability of exceedance). Following this method, Sr can be estimated from precipitation and evaporative demand data. The results of this â climateâ based methodâ are compared with traditional estimates from soil data for 32 catchments in New Zealand. The results show that the differences between catchments in climateâ derived catchment representative Sr values are larger than for soilâ derived Sr values. Using a model experiment, we show that the climateâ derived Sr can better reproduce hydrological regime signatures for humid catchments; for more arid catchments, the soil and climate methods perform similarly. This makes the climateâ based Sr a valuable addition for increasing hydrological understanding and reducing hydrological model uncertainty.Key Points:Plants develop their root systems to survive droughtsModel root zone storage capacity (Sr) can be inferred from climate recordsModel experiment shows that Sr is stronger influenced by climate than by soilPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137190/1/wrcr21890.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137190/2/wrcr21890_am.pd

Climate Change Impacts on Net Ecosystem Productivity in a Subtropical Shrubland of Northwestern México

The sensitivity of semiarid ecosystems to climate change is not well understood due to competing effects of soil and plantâ mediated carbon fluxes. Limited observations of net ecosystem productivity (NEP) under rising air temperature and CO2 and altered precipitation regimes also hinder climate change assessments. A promising avenue for addressing this challenge is through the application of numerical models. In this work, we combine a mechanistic ecohydrological model and a soil carbon model to simulate soil and plant processes in a subtropical shrubland of northwest México. Due to the influence of the North American monsoon, the site exhibits net carbon losses early in the summer and net carbon gains during the photosynthetically active season. After building confidence in the simulations through comparisons with eddy covariance flux data, we conduct a series of climate change experiments for nearâ future (2030â 2045) scenarios that test the impact of meteorological changes and CO2 fertilization relative to historical conditions (1990â 2005). Results indicate that reductions in NEP arising from warmer conditions are effectively offset by gains in NEP due to the impact of higher CO2 on water use efficiency. For cases with higher summer rainfall and CO2 fertilization, climate change impacts lead to an increase of ~25% in NEP relative to historical conditions (mean of 66 g C mâ 2). Net primary production and soil respiration derived from decomposition are shown to be important processes that interact to control NEP and, given the role of semiarid ecosystems in the global carbon budget, deserve attention in future simulation efforts of ecosystem fluxes.Key PointsModel simulation accurately captured the seasonality of vegetation activityNet ecosystem productivity decreased under reduced summer rainfall and increased temperature scenariosElevated CO2 scenarios offset the negative impacts of meteorological conditionsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142969/1/jgrg20992_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142969/2/jgrg20992.pd